The organic EL light-emitting device is a light-emitting device using electroluminescence of organic compound. The organic EL light-emitting device has sub-pixels (pixel regions) arranged on a substrate in a matrix arrangement, each having an organic light-emitting layer emitting red (R), green (G) or blue (B) light.
Organic compounds contained in the organic light-emitting layer producing electroluminescence are classified roughly into combinations of low-molecular organic compounds (host material and dopant material) and high-molecular organic compounds. Examples of high-molecular organic compounds producing electroluminescence include polyphenylene vinylene called PPV and derivatives thereof. The organic EL light-emitting device containing high-molecular organic compounds is driven at a relatively low voltage, consumes low electric power, and can provide a larger display screen. Accordingly, the organic EL light-emitting device using high-molecular organic compounds is actively researched these days.
For example, the organic light-emitting layer containing high-molecular organic compounds is formed by applying a material liquid containing an organic light-emitting material and a solvent onto a pixel electrode by the inkjet printing or other technique. Therefore, when ink containing an organic light-emitting material is applied to respective sub-pixels for the manufacture of an organic EL light-emitting device, it is necessary to prevent the ink from entering into a sub-pixel emitting a different color.
A method for applying ink to a color emission region is known. In this method, in order to prevent the ink from entering into a sub-pixel emitting a different color, a region having sub-pixels emitting the same color of light arranged in one row (hereinafter also referred to as a “color emission region”) is defined by a linear partition wall (bank), whereby the ink is applied to the color emission region (for example, see patent literature 1).
In the method for applying ink to a color emission region defined by linear banks as disclosed in patent literature 1, ink can freely move across the color emission region. Therefore, the organic light-emitting layer of a sub-pixel in the color emission region is leveled, and thereby the thickness of the organic light-emitting layer becomes uniform among the sub-pixels. This provides an organic EL light-emitting device with little brightness variation among pixels.
However, unless there is a barrier for separating sub-pixels in the color emission region as in the method disclosed in patent literature 1, it poses a problem that cross talk occurs between the sub-pixels in the color emission region, which reduces the contrast of the organic EL light-emitting device.
As a known method for solving the above problem, a second partition wall is arranged between sub-pixels in a color emission region (for example, see patent literature 2). FIG. 1 is a top view illustrating an organic EL light-emitting device disclosed in patent literature 2.
As shown in FIG. 1, the light-emitting device disclosed in patent literature 2 includes first partition walls 5 defining color emission regions, and second partition walls 7 arranged between sub-pixels 3 in the color emission regions. Further, adjacent sub-pixels 3 in the color emission region are connected via grooves 8 (a region in which no second partition wall is formed) formed between the first partition wall and the second partition wall.
By providing the second partition wall between adjacent sub-pixels in the color emission region in this way, crosstalk between the sub-pixels is reduced, whereby the contrast of the light-emitting device can be improved. Further, since the adjacent sub-pixels are connected via grooves, a material liquid applied in the color emission region can move between the adjacent sub-pixels, and thereby the thickness of the organic light-emitting layer becomes uniform among sub-pixels. As described above, according to the invention described in patent literature 2, not only the crosstalk can be reduced but also the the organic light-emitting layer can be leveled.
The organic light-emitting layer is formed by the coating method in a clean room, but it is impossible to completely rid the clean room of foreign substances such as particles derived from the surrounding environment and organic light-emitting layer production equipment. Therefore, foreign substances may be mixed in the sub-pixel during the steps for producing the organic EL light-emitting device.
A technique for making protrusions on a linear bank in order to prevent ink from entering into an adjacent color emission region is known (for example, see patent literature 3). The organic EL light-emitting device disclosed in patent literature 3 is a passive matrix type, in which a bank functions as a separator for a counter electrode.
In the active matrix type organic EL light-emitting device, a method for forming a groove in a bank in order to prevent a counter electrode from being divided by the bank is known (for example, see patent literatures 4 to 9). In the organic EL light-emitting devices disclosed in patent literatures 4 to 9, each sub-pixel is independently arranged on the organic light-emitting layer.